I've been going back through some pictures I took last month, trying to identify the birds in the pictures. I've found one gull that I'm having problems with. I've got a couple of shots I'm going to share with you, and then I'll give my current thoughts and reasoning.

The picture was taken on 23 Feb 09, on the grounds of Naval Air Station Pensacola. The gull on the right is the one I'm having difficulty with. The next picture is a closer view of that gull.

I'm reasonably certain that the gull on the left is a Ring-Billed Gull, and the gull on the left definitely seemed to be just a little smaller. The size, location, and most of the appearance of the gull on the left are consistent with a Laughing Gull. However, the dark half-hood is pretty extensive, and would seem to be a lot more consistent with a Franklin's Gull than a Laughing Gull. If I had just the picture of the gull, and no other information, I'd definitely be thinking Franklin's Gull.

The thing is, Franklin's Gulls are rare on the Gulf Coast of Florida, while Laughing Gulls are very common. What do you think? Is this a case of a novice birder hearing hoofbeats and thinking "zebra", or did I get lucky and actually spot a bird that's not common to the area?

Gulls can be challenging - good for you being cautious.
As a south FL birder (not a gull expert though), I would say laughing without even a second glance. They definitely can have a partial hood that looks like that - plumage is all over the place. So the starting assumption for me would be laughing, and I'd have to really feel like something's off to suspect Franklin's.
I did look in my field guide though, to make sure, and here's what I think you can use to confirm laugher:
1. The white spots on the the black wingtips should be much larger on a Franklin's.
2. Where the wing goes from gray to black, a Franklin's would have an obvious white band. This gull does not.
Ooh, GrrlScientist has a good picture of both: http://tinyurl.com/89zrhh
And yes on the ring-billed!

Just to confuse things a little more, here is a link to the USGS description of the ring billed gull which has a paragraph at the end comparing various juvenile and immature ring billed, laughing and Franklin's gulls.http://www.mbr-pwrc.usgs.gov/infocenter/i0580id.html
Also, I read elsewhere that they interbreed, so that throws another monkeywrench into the equation. I would hazard a guess that it was an immature laughing gull, but I am having a hard enough time identifying different sparrows and warblers, so take that with a grain of salt!
Corinne
Summerfield FL

Just to confuse things a little more, here is a link to the USGS description of the ring billed gull which has a paragraph at the end comparing various juvenile and immature ring billed, laughing and Franklin's gulls.http://www.mbr-pwrc.usgs.gov/infocenter/i0580id.html
Also, I read elsewhere that they interbreed, so that throws another monkeywrench into the equation. I would hazard a guess that it was an immature laughing gull, but I am having a hard enough time identifying different sparrows and warblers, so take that with a grain of salt!
Corinne
Summerfield FL